Abstract
An experimental study has been performed in order to investigate the relationship between the extensional viscosity of polymers and the turbulent drag reduction.Polyethyleneoxide as a flexible polymer and hydroxypropyl cellulose as a rigid rod-like polymer were added to the two-dimensional turbulence that was visualized by the interference pattern of the flowing soap films and analyzed by an originally-developed single-image analysis.The power spectra of interference images were obtained,which is related to the water layer fluctuations in turbulence.The power spectra show a scaling behaviour and the power components give the information of drag reduction.Wavelet-coefficient was also calculated.It was found from these results that the energy transfer mechanisms are different in streamwise and normal directions.In the normal direction,the energy transfer is prohibited by the orientation of polymers,while the energy transfer in the streamwise direction is prohibited by extensional viscosity of polymers.The characteristic scales for the energy transfer were also observed as a periodic structure in Wavelet-coefficients.
